1. There will be five lines of research comparing the behaviors of young (3 yr) very old (26 yr). and less old (18-20 yr) rhesus monkeys. It will include studies of: 1. Behavioral Rigidity. Informational analysis indicates greater stereotypy of the temporal organization of behavior of old than young monkeys. Attempts will be made to break up highly probable sequences of behavior and arbitrarily make selected obscure behaviors adaptive. This line of research could provide an animal model of senile rigidity and suggest strategies for measuring and coping with rigidity in old human beings. 2. Habituation. Since profiles of ongoing behavior differ with a monkey's age the rate of habituation of selected behaviors should also differ. Examining this possibility would also allow investigation of the generalization of habituation from one response to another and possible inferences about the underlying mechanisms. 3. Adjunctive Behaviors. Recent work at this laboratory on variable interval schedules suggests different patterns of schedule induced behaviors in young and old monkeys. This will be pursued further with special attention to self-directed and aggressive behaviors. 4. Performance Measures. Further attention will be given to methods of assessing steadiness and work output in old and young monkeys. 5. Cognative Tasks. Repetitions of rewarded and nonrewarded stimuli differently effect memory by monkeys. Experiments are designed to determine whether or not this effect interacts with the age of the subject. BIBLIOGRAPHIC REFERENCES: Medin, D.L. and Davis, R.T. Memory. In A.M. Schrier and F. Stollnitz (Eds.), Behavior of nonhuman Primates: Modern Research Trends, Vol. 5, New York: Academic Press, 1974.